{-# LANGUAGE CPP #-}
#ifndef HASKELL98
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
# if __GLASGOW_HASKELL__ >= 704
{-# LANGUAGE Safe #-}
# elif __GLASGOW_HASKELL__ >= 702
{-# LANGUAGE Trustworthy #-}
# endif
# if __GLASGOW_HASKELL__ >= 706
{-# LANGUAGE PolyKinds #-}
# endif
#endif
-- |
-- Module : Data.Functor.Reverse
-- Copyright : (c) Russell O'Connor 2009
-- License : BSD-style (see the file LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : portable
--
-- Making functors whose elements are notionally in the reverse order
-- from the original functor.
--
-- /NB:/ Note this module is only included in @lens@ for backwards
-- compatibility with older @containers@ versions.
module Data.Functor.Reverse where
import Control.Applicative.Backwards
import Data.Functor.Classes
import Prelude hiding (foldr, foldr1, foldl, foldl1)
import Control.Applicative
import Control.Monad
#if MIN_VERSION_base(4,9,0)
import qualified Control.Monad.Fail as Fail
#endif
import Data.Foldable
import Data.Traversable
import Data.Monoid
#ifndef HASKELL98
# ifdef GENERIC_DERIVING
import Generics.Deriving.Base
# elif __GLASGOW_HASKELL__ >= 702
import GHC.Generics
# endif
#endif
-- | The same functor, but with 'Foldable' and 'Traversable' instances
-- that process the elements in the reverse order.
newtype Reverse f a = Reverse { getReverse :: f a }
#ifndef HASKELL98
# if __GLASGOW_HASKELL__ >= 702 || defined(GENERIC_DERIVING)
-- Generic(1) instances for Reverse
instance Generic (Reverse f a) where
type Rep (Reverse f a) = D1 D1'Reverse (C1 C1_0'Reverse (S1 S1_0_0'Reverse (Rec0 (f a))))
from (Reverse x) = M1 (M1 (M1 (K1 x)))
to (M1 (M1 (M1 (K1 x)))) = Reverse x
instance Generic1 (Reverse f) where
type Rep1 (Reverse f) = D1 D1'Reverse (C1 C1_0'Reverse (S1 S1_0_0'Reverse (Rec1 f)))
from1 (Reverse x) = M1 (M1 (M1 (Rec1 x)))
to1 (M1 (M1 (M1 x))) = Reverse (unRec1 x)
instance Datatype D1'Reverse where
datatypeName _ = "Reverse"
moduleName _ = "Data.Functor.Reverse"
# if MIN_VERSION_base(4,7,0)
isNewtype _ = True
# endif
instance Constructor C1_0'Reverse where
conName _ = "Reverse"
conIsRecord _ = True
instance Selector S1_0_0'Reverse where
selName _ = "getReverse"
data D1'Reverse
data C1_0'Reverse
data S1_0_0'Reverse
# endif
#endif
instance (Eq1 f) => Eq1 (Reverse f) where
liftEq eq (Reverse x) (Reverse y) = liftEq eq x y
{-# INLINE liftEq #-}
instance (Ord1 f) => Ord1 (Reverse f) where
liftCompare comp (Reverse x) (Reverse y) = liftCompare comp x y
{-# INLINE liftCompare #-}
instance (Read1 f) => Read1 (Reverse f) where
liftReadsPrec rp rl = readsData $
readsUnaryWith (liftReadsPrec rp rl) "Reverse" Reverse
instance (Show1 f) => Show1 (Reverse f) where
liftShowsPrec sp sl d (Reverse x) =
showsUnaryWith (liftShowsPrec sp sl) "Reverse" d x
instance (Eq1 f, Eq a) => Eq (Reverse f a) where (==) = eq1
instance (Ord1 f, Ord a) => Ord (Reverse f a) where compare = compare1
instance (Read1 f, Read a) => Read (Reverse f a) where readsPrec = readsPrec1
instance (Show1 f, Show a) => Show (Reverse f a) where showsPrec = showsPrec1
-- | Derived instance.
instance (Functor f) => Functor (Reverse f) where
fmap f (Reverse a) = Reverse (fmap f a)
{-# INLINE fmap #-}
-- | Derived instance.
instance (Applicative f) => Applicative (Reverse f) where
pure a = Reverse (pure a)
{-# INLINE pure #-}
Reverse f <*> Reverse a = Reverse (f <*> a)
{-# INLINE (<*>) #-}
-- | Derived instance.
instance (Alternative f) => Alternative (Reverse f) where
empty = Reverse empty
{-# INLINE empty #-}
Reverse x <|> Reverse y = Reverse (x <|> y)
{-# INLINE (<|>) #-}
-- | Derived instance.
instance (Monad m) => Monad (Reverse m) where
return a = Reverse (return a)
{-# INLINE return #-}
m >>= f = Reverse (getReverse m >>= getReverse . f)
{-# INLINE (>>=) #-}
#if !(MIN_VERSION_base(4,13,0))
fail msg = Reverse (fail msg)
{-# INLINE fail #-}
#endif
-- | Derived instance.
instance (MonadPlus m) => MonadPlus (Reverse m) where
mzero = Reverse mzero
{-# INLINE mzero #-}
Reverse x `mplus` Reverse y = Reverse (x `mplus` y)
{-# INLINE mplus #-}
-- | Fold from right to left.
instance (Foldable f) => Foldable (Reverse f) where
foldMap f (Reverse t) = getDual (foldMap (Dual . f) t)
{-# INLINE foldMap #-}
foldr f z (Reverse t) = foldl (flip f) z t
{-# INLINE foldr #-}
foldl f z (Reverse t) = foldr (flip f) z t
{-# INLINE foldl #-}
foldr1 f (Reverse t) = foldl1 (flip f) t
{-# INLINE foldr1 #-}
foldl1 f (Reverse t) = foldr1 (flip f) t
{-# INLINE foldl1 #-}
-- | Traverse from right to left.
instance (Traversable f) => Traversable (Reverse f) where
traverse f (Reverse t) =
fmap Reverse . forwards $ traverse (Backwards . f) t
{-# INLINE traverse #-}
sequenceA (Reverse t) =
fmap Reverse . forwards $ sequenceA (fmap Backwards t)
{-# INLINE sequenceA #-}